Devices are known for printing webs of paper in which the machines for printing webs of paper are generally fed by a spool of paper mounted on an unwinder and from which the web of paper is drawn with the aid of a dispenser. The printing of such a web of paper is carried out by passing this web through one or more printing units then through a hot air drier and through a set of cooling rollers in order to fix the film of ink on the web of paper. Subsequently, the printed web of paper is folded at its middle along a longitudinal direction by a folding device commonly known to a person of ordinary skill in the art as a kite. The longitudinally folded web of paper is cut up into copies between two cylinders, a transfer cylinder and a cutting cylinder.
A first transverse folding of the copies is carried out between the transfer cylinder equipped with engaging blades and a folding cylinder equipped with jaws. The copies coming from the folding cylinder folded perpendicularly to their direction of forward travel, are held and transported by two sets of belts situated respectively above and below the copies.
In order to fold a folded copy for a second time, along a fold perpendicular to the first fold produced, a longitudinal folding device called a quarter fold is used which forms a fold parallel to the direction of forward travel of the copy. In this case, the copies are transported by the belts as far as the quarter fold on a longitudinal folding table comprising a longitudinal slit.
The quarter fold device includes an engagement blade of known type placed above the longitudinal slit and moving alternately upwards and downwards in order to introduce the paper copy into the slit. It also includes, below the longitudinal slit, two folding rollers whose geometric axes of rotation are parallel to the slit. These two rollers rotate in opposite directions so as to create a drawing-in space between them. A copy engaged in the slit is drawn into the space and folded between the two rollers, then leaving the rollers at a speed equal to the superficial rotational speed of the rollers.
A device known as a fan, well known to a person of ordinary skill in the art, receives the folded copies leaving the rollers. The fan slows down the copies and places them one after the other on a receiving belt moving slowly so that the copies partially overlap one another forming a sheet.
These conventional quarter folding devices, however, exhibit certain drawbacks. For one, when a copy is engaged in the slit by the engagement blade, it is drawn in abruptly at the speed of the folding rollers. In the case of a thin paper copy, the contact between the rollers and the paper is insufficient, and for this reason the copy slides on the surface of the rollers.
Another drawback with the prior art devices is that upon leaving the folding rollers, a copy retains the speed of the rollers and must be slowed down in the fan or like device. During the transfer of the copy from the quarter fold to the fan, the copy may tear and/or become wedged.